linux-kernel - Re: [PATCH v2] mm/page_alloc: remove unnecessary order check in __alloc_pages_direct

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Message-ID: <CAKTCnzk1GZ+=ijvOm=Tw1GNGLdefovvS5wsR9XqpLLmrSSx9=g@mail.gmail.com>
Date:	Wed, 15 Jun 2016 19:40:40 +1000
From:	Balbir Singh <bsingharora@...il.com>
To:	Ganesh Mahendran <opensource.ganesh@...il.com>
Cc:	linux-mm <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Joonsoo Kim <iamjoonsoo.kim@....com>, mhocko@...e.com,
	mina86@...a86.com, Minchan Kim <minchan@...nel.org>,
	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2] mm/page_alloc: remove unnecessary order check in __alloc_pages_direct_compact

On Wed, Jun 15, 2016 at 7:34 PM, Ganesh Mahendran
<opensource.ganesh@...il.com> wrote:
> In the callee try_to_compact_pages(), the (order == 0) is checked,
> so remove check in __alloc_pages_direct_compact.
>
> Signed-off-by: Ganesh Mahendran <opensource.ganesh@...il.com>
> ---
> v2:
>   remove the check in __alloc_pages_direct_compact - Anshuman Khandual
> ---
>  mm/page_alloc.c | 3 ---
>  1 file changed, 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b9ea618..2f5a82a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3173,9 +3173,6 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
>         struct page *page;
>         int contended_compaction;
>
> -       if (!order)
> -               return NULL;
> -
>         current->flags |= PF_MEMALLOC;
>         *compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac,
>                                                 mode, &contended_compaction);

What is the benefit of this. Is an if check more expensive than
calling the function and returning from it? I don't feel strongly
about such changes, but its good to audit the overall code for reading
and performance.

Balbir Singh